In point-to-multipoint aggregation type network, as illustrated in FIG. 1, an Access Gate (AG) uplink provides two Fast Ethernet (FE) interfaces, the active and the standby. During normal operation, services are available only on the active port, while no service is available on the standby port. The two FE ports of the Access Gate are connected to the two different ports of an access device A. Each Access Gate takes up two service network channels independently via the access device. The active channel provides an active router via an aggregation device C1, while the standby channel provides a standby router via an aggregation device C2. The active router and the standby router are connected by fiber directly, running Virtual Router Redundancy Protocol (VRRP). The aggregation devices C1 and C2 are connected by a Virtual Concatenation Group (VCG) channel or by a Gigabyte Ethernet (GE).
User data may have access to the service network via access devices A1, A2, and A3. When aggregated to aggregation devices C1 and C2, the user data may access to a Wide Area Network or a core network via the active router and the standby router, wherein the VRRP protocol is carried out between the active router and the standby router. The VRRP protocol may orchestrate a group of routers into a virtual router, referred to as a standby group. Such virtual router has its own IP address. The host in the network communicates with other network via this virtual router. If the active router in the standby group fails, the other standby routers in the standby group may become to be the new active router and continue to provide routing service for the host in the network.
As shown in FIG. 1, in normal condition, Access Gates AG1, AG2, and AG3 reach the aggregation device C1 via access device A1, A2, A3 and the active link, and finally arrive at the active router to complete the communication process. When the link between the active router and the aggregation device C1 fails, the communication between the active router and all access gates will be interrupted. At this moment, the standby network or link has to be enabled so as to ensure a normal transmission of the important data. As illustrated in dashed line, the standby link in the instance of FIG. 1 includes FE links between the access gates AG1, AG2, AG3 and the access device A1, A2, A3, and standby channels between the access device A1, A2, A3 and the aggregation device C2. The standby communication may also be carried out using the standby network. As illustrated in FIG. 2, the communication between the access gate AG3 and the aggregation device C2 may be carried out using Access device A4 and the aggregation device C3, or service network 2.
In point-to-multipoint network, when the partial or entire access point link (active link between the access gate and the access device) fails, the user access gate is able to detect the failure in the link and enables a standby link or network. The communication is conducted between the standby link or network and the aggregation device. The aggregation device does not need to be informed of the failure of the access link or network.
In point-to-multipoint network, if the aggregation device fails, the access device fails to know about the failure. If the access device still uses the original network to conduct communication, it turns out that the communication between the access gate and the aggregation device will be in a disconnected state.
In point-to-multipoint network, when the service network fails, the active router and the access gate fails to know about the failure. If the active router and the access gate still use the active link to conduct communication, the communication may be interrupted.
With respect to the above problems, prior art provides a technique for solving the link path through problem in point-to-point simple network. For symmetric point-to-point network, the principle and the implementation of such technique can be described as follows. The service device detects if any failure occurs on the Ethernet port link and the network link. When a failure occurs, the service device employs a control frame to pass the link failure information to the remote service device. The remote service device disconnects the user link and performs a corresponding processing in response to the received control frame containing the link failure information. The user at the failure end and the user at the remote end communicate through the standby network. When the link is repaired, the service device at the repaired end sends a control frame containing the link repaired information to the service device at the remote end and rebuilds the communication between the users along the original link. The technique does not differentiate the service devices of the two ends. As long as a failure occurred at one end, the other end will disconnect the link connected to the user for sure.
In FIG. 1, when a link or network failure occurs in the aggregation device C1, the access devices A1, A2 and A3 do not know about the failure in the uplink and may still use the active link to conduct communication. As a result, all the services between the access gates and the active router may be interrupted; even using point-to-point Link Pass Through (LPT) technique may not be able to inform multiple access points of the link status. When a link or network failure occurs in parts of the access devices, point-to-point LPT technique may inform the aggregation device of the link status of the access device. If the aggregation device disconnects the connection with the router after receiving notification of the link status, the services of the access devices where no link failure occurs may also be interrupted.
Point-to-point LPT technique can not be applied to point-to-multipoint network. The existing LTP technique only passes link status of two users or devices in the point-to-point network. The technique cannot be used to pass link status in aggregation type network when failures occur in multiple places or networks.